The invention is directed to a communication system for transmission of message cells according to an asynchronous transfer mode during the course of virtual connections. It has hitherto been provided in communication systems working according to an asynchronous transfer mode (ATM) that either the message cell traffic established by message cell streams of a plurality of subscriber equipment units are concentrated by a few, large, central concentrators, as a result whereof long, poorly utilized subscriber lines can arise between the subscriber equipment and the respective concentrator, or that a plurality of concentrators are established at a closer distance to the subscriber equipment, these being only capable of achieving a poor concentration because of only a few connected subscriber equipment units.
A further possibility is comprised in the employment of ATM concentrators and ATM multiplexers with add/drop functionality in a star or ring topology which concentrate or multiplex the message cell traffic established by different message cell streams onto different bundles or virtual paths with fixed band widths. Many small bundles or paths that, given the same blocking probability, are more poorly used than large bundles or paths, thus arise. An arrangement of concentrators in a ring topology of a communication system is already known ("Communication Switching Systems", Murry Rubin and C. E. Haller, Reinhold Publishing Corporation, N.Y., 1966, pages 218 and 219). In this known arrangement, two separate ring line systems connected to one another via a central processor are provided, a plurality of concentrators being respectively inserted into each of these. A plurality of subscriber equipment units are respectively connected to the individual concentrators. A message transmission between the subscriber equipment units and the central processor thereby occurs according to an inquiry/reply principle, whereby the message signals are transmitted in a free flow on an arbitrary basis without monitoring by the central processor. Beyond this, superimpositions of message signals as a consequence of disturbances are to be prevented by switch and memory means respectively present in the concentrators.